Investigation of the "R" tumor margin classification and prognostic factors in apocrine gland anal sac adenocarcinoma of dogs.

Abstract

Objective: The aim of this retrospective study was to investigate the relative frequency of R0 margin classification following excision of canine apocrine gland anal sac adenocarcinoma (AGASACA). Secondary aims were to establish if R0/R1 margins, or other dog or tumor characteristics, were prognostic.

Study design: Retrospective cohort study.

Sample population: Seventy-four dogs that underwent AGASACA excision.

Methods: Each tumor margin was classified as R0 or R1 from the histopathology report. Additional data relating to primary tumor characteristics, preoperative assessment, local recurrence, metastases and survival were collated from the medical record.

Results: The rate of R0 margin classification following AGASACA excision was 75.7%. An R1 margin classification was associated with increased risk of local recurrence (OR 23, p < .0001). Overall median survival time following surgery was 25 months (95% CI 21-33). Survival time was reduced in dogs with preoperative hypercalcemia (7.5 months, p = .012), presence of metastatic disease (17 months, p = .005) and lymphovascular invasion on histopathology (21 months, p = .021). Mitotic count (p = .0069) and absence of adjunct therapy (p = .0247) also reduced survival time.

Conclusion: The R margin classification was clinically useful in predicting local recurrence. Preoperative hypercalcemia, lymphovascular invasion on histopathology, presence of metastatic disease, mitotic count, and absence of adjunct therapy all negatively affected survival.

Clinical impact: Achieving complete margins was feasible in most dogs undergoing AGASACA excision and reduced the risk of local recurrence. The R margin classification scheme was clinically useful when reporting histopathology of canine AGASACAs.